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Fetal Length Calculator

calculate fetal length for free

* Femur Length (FL) - Measures the longest bone in the body and reflects the longitudinal growth of the fetus. It increases from about 1.5 cm at 14 weeks to about 7.8 cm at term.

Femur length (FL) : mm

The Fetal Length Calculator calculates the length of a baby in the womb according to the length of a baby’s femur. Therefore, you shouldn’t worry if your doctor doesn’t tell you how long is your baby after an ultrasound. By using this calculator, you can find out that information with just a few clicks. 

How to use the Fetal Length Calculator?

Calculating of fetal length is very simple with our calculator. Just look at the ultrasound report that you get from the doctor. There are some measurements marked with AC, FL, BPD, HC. In order to calculate fetal length, you will need only the FL measurement, which represents the length of the femur. Enter the FL measurement in the highlighted box above and then get the length of your baby.

Why is it important to measure fetal length?

The fetal length is very important information in prenatal diagnosis. It indicates the health of a baby. A fetal length that deviates from the average may indicate dwarfism, some genetic disorders such as Down’s and Patau’s syndrome or placental problems. 

However, if the ultrasound shows that your baby’s length is not in line with average, you shouldn’t panic immediately. I’ll explain to you why you should stay calm by giving you possible reasons for such a deviation.


The deviation of the fetal length from the average is usually only due to genetics. Actually, it is normal that baby has low growth if some from baby’s parents are low growth.

Also, it is often a case that a doctor makes an error in the ultrasound measurement. This is especially possible if the baby took an awkward position during the ultrasound, which reduced the precision of the measurement.

Furthermore, it is possible that you aren’t well-defined for your pregnancy, so the doctor looks at measures for the week you think you are currently in, while you are actually a week and maybe two behind.

In the end, there is also a chance that a baby late in growth at some point and reaches the expected length already on the next measurement. Therefore, making a diagnosis based on a single measurement is completely ridiculous. More measurements, more time, and additional testing are needed to determine a baby’s true condition.


As we can see, the fetal length is a good indicator of a baby’s health and development. Nevertheless, it is not itself an indication that a baby has some health problems. What may indicate a problem is the combination of a short fetal length with other bad findings, such as double and triple test results, etc.

Certainly, if your findings show deviations in fetal length relative to the average length for a given week of pregnancy, it is best to speak with your doctor. As someone who guides your pregnancy, he will be able to give you the most realistic picture of your baby’s health and your health as well.

The Recommendation

If you want to calculate the weight of your baby, you can use our Fetal Weight Calculator. Also, in order to find out whether the length and weight of your baby are in line with the baby average growth in the same gestation week, see The Fetal Growth Chart


3 thoughts on “Fetal Length Calculator

  1. I need to check the weight of my baby also. You should make the fetal weight calculator too… I don’t want to go on other sites to check that. I like this very much… You are excellent! :-*

  2. I come here to calculate the length of my baby after every ultrasound… Thank for this calculator!

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